Method of producing finely divided metallic layers



Sept. 27, 1938. G. LIEBMANN v 2,131,187

METHOD OF PRODUCING FINELJY DIVIL'EE) METALL IC LAYERS File d May 28,1955 717 yen for I WIEMMM ATENT orrics v METHQD F PRODUCING FINELYDIVIDE METALLIC LAYERS Gerhmd Liebmann, Berlin, Germany Application May28, 1935, Serial No. 23,845

- In Germany May 31, 1934 9 Claims. (01. 91-701) The present inventionrelates to a methodof producing metallic layers on insulating materials,such, for example, as mica or the like, whereby the metallic layerconsists of the finest particles,

which are insulated against each other, and represents in a manner ofspeaking a mosaic screen composed of single particles of metal. A screenof this nature may be employed more particularly in certain televisionimage recording methods, in

in which the images to be transmitted are recorded with the assistanceof an Ikonoscope camera. After corresponding treatment the mosaic screenrepresents a surface collection of elementary photo-cells, which produceelectrical charges corld responding with the particular exposure. Thesecharges may then further be employed for controlling the transmitter insuitable fashion.

The production oi the layer consisting of finest particles of metal isaccompanied by considerable 2o dimcultles, both as regards selection ofthe mate-1 rial for the intermediate insulating layer as well as themethod of insulation.

It is possible to employ mica for the intermediate insulating layer. 95when employing a heating process for dividing the case of chemicaltreatment 'it is impossible in numerous cases, owing to the smallpowers.of

adhesion, to produce a metallic layer in equal I Y replaced to a.certain extent by a suitable temdistribution.

5 The methods set forth in the present invention are devoid of thesedisadvantages.

According to the invention, there are employed as intermediatedielectric layers, sheets of mica or other suitable bases, for example,ceramicmagig terial, certain kinds of glass, etc., the surface of thisbase preferably being made smooth by polish ing. On this base there isproduced in suitable fashion a metallic coating, for example a silver,copper or the like coating. A metallic coating as of this nature may beproduced, for example, chemically by cathode atomization or by thermalapplication in vapour form. The metallized plates are then heated to ahigh temperature in an atmosphere 0;? indifierent gas or in a vacuum. soIf the metallic coating is of a certain thickness (no longertransparent), the temperature is required to be very high, for examplein the case of silver to about 100W, in order to obtain a brief fusingof the layer of silver, whereby the surface s5 is then converted fromthe previously unitary The use of thismaterial v I An, additional methofo insular formation a metallic layer into single elementary partsisconfronted by diificulties owing to the inconstancy structurelessmetallic surface into a very even mosaic consisting of small drops ofmetal of negligible diameter and insulated against each other. Accordingto the invention, this heating is performed extremely rapidly,preferably bymeans of perature constancy of mice. is of advantage when,

employing-a materialof this kind; Whenuslng other materials, such asceramic substances, glass or the like, the surface ofithe base; ispreferably 'madesmooth by polishing, in order to accelerate the insularformation during the heating process.

According to the'invention,' it isalso possible to deposit the metalliclayerlon a heated base, so that small globules ,1 are likewise formedright from the commencemenitj ,When using mica, however, the method-Jojdepositedmetal f subsequently heating the Srl in preferred.

resides according to 1th: invention in the fact the above is to be thats. thin layer of silvendeposited, for example,

sure (approximately 1 mm. mercury). Theolternate oxidation and reductionmight also be ture is thereupon again lowered, etc. In the case 40 ofthe glow discharge method the silver layer to "on mica isaltemately-oxidi'zedand reduced. This method is performed in themostfconvenient form by glow discharge in anatmosphere of alternately"introduced oxygen and hydmg'enjat suitable presbe granulated is in themost convenient form the layer than at other points. As final stage ofthe process, after production of the discrete particles of silver, thereis conveniently performed a light oxidation, as in this man'nerit ispossible to obtain a layer which is advantageously suited v for photosensitization.

The drawing shows-diagrammatically how to carry out the method accordingto the invention. In the drawing Fig. 1 shows the indirect heating bymeans of a heating plate I, which heats by radiation the layer of silverI mounted on the supporting material 3, for example mica. Since thisheating is required to commence instantaneously. the heating ispreferably performed by eddy currents, which is representeddiagrammatically by the high-frequency coil 4.

Fig. 2 shows the arrangement for carrying out the glow dischargeprocess. In the same there is provided an electrode 5, which isconnected up as anode and is situated opposite to a grid-like cathode I.The metallic layer 1 to be granulated is arranged within reach of theglow discharge which develops in the case of a suitable filling of gas.'1 is the metallic layer on the base 0. In

Figs. 3 and 4 there is illustrated by way of example thefinishedproduct. In these I is the intermediate di-electric'layer, whichacts for the coatings l0 and H. The coating ll represents,

the thin layer of metal divided up into finest elementary particles,whilst I I is intended as capac-' itative counter-coating for thephotocell arrangement.

The following special embodiments of the present invention have beenproved useful:

A well-cleaned mica plate with all grease removed is coated by thethermal vaporization of silver with a silver layer ofapproximately liq-A0 1 in thickness. A thickness of the layer approximately midway of thestated range, 1. e., approximately $5 to H w produced the best results.The application of the layer by vaporization performed in a suitablevessel from which the air has been removed, the distance between themica plate to be treated and the evaporation furnace being of suchextent that a very even coating is obtained. Insulation edges-of adesired kind may be allowed to remain by selective screening. After theapplication 'of the silver layerby vaporization has been completed acertain amoimt of air or oxygen is allowed to enter the vessel, and thepart of the vessel in which the plate is situated, is heatedto atemperature below 500 C.

I approximately 400-450 C. This latter operation extends over a periodof approximately 15 to 30 minutes. After cooling-it will be noticed thatthe coating on the plate has been divided into single well-separatedcrystals of about In in size.

It has been'found that to obtain this effect it is necessary v 1. Toadhere to the above stated range as regards the thickness of the layer,and 2. To employ a suitable gas atmosphere. If the initial layer is madethinner, a granula tion" of any kind is not to be determined with theusual optical means available. If thelayer is too thick, there iscertainly a granulation up to a certain point, but the particles aresituated so close together that the requisite insulation may be not Iobtained. If on-the other hand the layeris still thicker (completelyopaque), a distribution according to the described process may be notac-.

1,000 (7.), andconsiderable difiiculties are then 1 encountered inpreventing the mica from becoming entirely useless. The size of theformed particles is also a wholly different one in the last mentionedcase. Further, it has been found that even with suitable layers aseparation does not take place when the process is performed in anextremely high vacum (higher than 10- mm. Hg). The presence of a certaingas atmosphere (presumably oxygen) is accordingly necessary for thesaparation at the low temperature stated.

Mica plates of this kind, which are furnished with a silver screen inthe manner stated, may then be employed in the known fashion, bysilvering the rear side and by oxidation and sensitization of the frontscreen surface, as lightsensitive mosaic electrodes in televisiontransmission tubes, more particularly tubes known'under the name ofIkonoscope.

I claim: a

1. A process of producing a finely subdivided metallic layer on aninsulating base comprising the steps of coating said base with silver,of interrupting coating actionwhen a layer of 0.01 to 0.1 -thickness hasbeen formed, and of subjecting the coated base to a thermal treatment ina gas atmosphere containing oxygen at a temperature of at least about400 centigrade and below 500 centigrade.

2. A process of producing a finely subdivided metallic layer on aninsulating base comprisin the steps of coating said base with silver, ofinterrupting this coating action when a layer of 0.01 to 0.1 a thicknesshas been formed, and of subjecting the coated base to a thermaltreatment in a gas atmosphere containing oxygen at a temperature of atleast about 400 centigrade and below 600 centigrade during 15 to 30minutes 3. A process of .producing a finely subdivided metallic layer onan insulating base comprising a temperature of 400 to 450 centigrade.

4. A process of producing a finely subdivided metallic layer 'on aninsulating base comprising the steps of coating said base with sliver,of interrupting this coating action when a layer of 0.01 to 0.1 athickness has been formed, and of subjecting the coated base to athermal treat-' ment in a gas atmosphere containing oxygen at 'atemperature ofat least about 400 centigrade and below 500 centigrade bycausing the radiation of a plate heated by eddy currents to act on saidcoated base. 4

5. A process of producing a finely subdivided metallic layer on a micabase comprising the steps of coating said base with sliver, ofinterrupting this coating action when a layer of 0.01 to 0.1 a thicknesshas been formed, and of subiecting the coated base to a thermaltreatment in a gas atmosphere containing oxygen at a temperature of atleast about 400 centigrade and below 500 centigrade.

8. A process of producing a-finely subdividedmetallic layer on a glassbase comprising the steps of coating said base with sliver, ofinterrupting this coating action when a layer of 0.01 to 0.1 thicknesshas been formed, and of sub- Jecting the coated base to a thermaltreatment in a gas atmosphere containing oxygen at a temperature of atleast about 400 centigrade and below 500' centigrade.

. 7. A process of producing a finely subdivided I metallic layer on abase of a'ceramic material comprising the steps of coating said basewithsilver, of interrupting this coating action when I.

a layer oi 0.01 to 0.1 a thickness has been formed. and of subjectingthe coated base to a thermal treatment in a gas atmosphere containingoxygen at a temperature oi at least about 400 centigrade and below 500'centigrade.

8. A process of producing a finely subdivided metallic layer on a glassbase comprising the steps 01' polishing the surface of said base. ofcoating the poiished-suriace oi. said base with silver, of interruptingthis coating action when a layer of 0.01 to 0.1 a thickness has beenformed, and of subjecting the coated base to a thermal treatment in agas atmosphere containing oxygen at a temperature or at least about 400'centigrade and below 500 centigrade.

9. A process of producing a finely subdivided metallic layer on a baseof ceramic material comprising the steps 01 polishing the surface ofsaid base, oi coating the polished surface of said base with silver, 01interrupting this coating action when a layer of 0.01 to 0.1 a thicknesshas been formed, and 0t subjecting the coated base to a thermaltreatment in a gas atmosphere containing oxygen at a temperature of atleast about 400 centigrade and below 500 centigrade.

GERHARD LIEBMANN.

